This application is based on and incorporates herein by reference Japanese Patent Applications No. 2000-25196 filed on Feb. 2, 2000 and No. 2000-344894 filed on Nov. 13, 2000.
The present invention relates to a clutch that allows rotation of a driven-side rotator while making the driven-side rotator difficult to rotate and also to a motor having such a clutch.
A motor of a power window system has a motor main body and an output unit. The output unit transmits rotation of a rotatable shaft of the motor main body to a regulator (located on a driven side) via a worm shaft to reduce a rotational speed of the rotatable shaft before it is transmitted to the regulator. The worm shaft is formed integrally with the rotatable shaft or is arranged coaxial with the rotatable shaft. When the motor is driven, the rotation of the rotatable shaft is transmitted to the output unit via the worm shaft. After the output unit reduces the rotational speed of the rotatable shaft, the regulator converts the rotational movement to reciprocal movement. As a result, a window glass is moved up and down by the regulator to close and open the window glass, respectively.
In this type of power window system, when the motor is not driven, a downward load applied to the window glass is converted to a rotational force by the regulator and is transmitted to the rotatable shaft of the motor main body to rotate the same. This transmission of the rotation causes forceful downward movement of the window glass to open the same when an external force is applied to the window glass, causing likelihood of burglarization.
In order to prevent such transmission of the rotation, a motor having a clutch that prevents the transmission of the rotation from a driven-side rotator to a driving-side rotator has been proposed. In this motor, the clutch transmits the rotation of the driving-side rotator to the driven-side rotator but does not transmit the rotation of the driven-side rotator to the driving-side rotator.
It would be easier and better if the clutch is designed such that the transmission of the rotation from the driven-side rotator to the driving-side rotator is prevented by the entire motor or by the entire power window system in consideration of loss of the rotational force at each sliding portion within it. However, the above prior art prevents the transmission of the rotational force from the driven-side rotator to the driving-side rotator only by the clutch itself. Thus, in order to completely prevent the transmission of the rotational force from the driven-side rotator to the driving-side rotator only by the clutch, each component of the clutch must be manufactured with a high degree of accuracy, resulting in the higher costs. As a result, there is a need for an inexpensive clutch that makes the rotation of the driven-side rotator difficult instead of completely preventing the transmission of the rotational force from the driven-side rotator to the driving-side rotator.
This fact is not only in the clutch used in the power window system but is also equally in any other devices that require a clutch and also require the rotation of the driven-side rotator to be allowed while making the rotation of the driven-side rotator difficult.
It is therefore an objective of the present invention to provide a clutch that transmits rotation of a driving-side rotator driven by a drive source to a driven-side rotator and that allows the rotation of the driven-side rotator while making the driven-side rotator difficult to rotate when the driven-side rotator is rotated by a load applied to it.
It is another objective of the present invention to provide a motor having such a clutch.
To achieve the above objectives, there is provided a clutch including a housing, a driving-side rotator, a driven-side rotator and a clampable element. The housing is non-rotatably secured and has an inner circumferential surface. The driving-side rotator is connected to a drive source and is rotatably received within the housing. The driven-side rotator is connected to a load and is rotatably received within the housing. Furthermore, the driven-side rotator is connected to the driving-side rotator in a manner allowing relative rotation of the driven-side rotator within a predetermined range in a rotational direction. The clampable element is arranged between the driven-side rotator and the inner circumferential surface of the housing and is positionable between a clamped position where the clampable element is clamped between the driven-side rotator and the inner circumferential surface of the housing and a non-clamped position where the clampable element is not clamped between the driven-side rotator and the inner circumferential surface of the housing.
When the driving-side rotator is rotated, rotation of the driving-side rotator causes the clampable element to be positioned in the non-clamped position and also to be revolved therewith. At the same time, the driving-side rotator engages the driven-side rotator in a rotational direction and transmits a rotational force of the driving-side rotator to the driven-side rotator. When the driven-side rotator is rotated, the clampable element is positioned in the clamped position, and at the same time the driven-side rotator is allowed to rotate while generating a desired frictional force between the clampable element and the inner circumferential surface of the housing.
Furthermore, there is also provided a motor having the above clutch.